None of Mondrian's paintings done in the "mature" late style were landscape orientation (all were portrait, square or diamond) so the true shitty mondrian generator would want to start there.
The "maturity" of that late work got me thinking about Mondrian's flower paintings and drawings, which he continued doing while he was making the primary colored rectangles. Legend has it he made these as his bread and butter since the rectangles weren't selling. I have always perversely wanted to see a retrospective that hung the artist's works in strict chronological order, to explode the myth of his development as a Modernist. (Suffice it to say the last one I saw at MOMA didn't do that.)
Even accomplishing that would be tricky, because many of the flowers aren't dated, or were clumsily back-dated by the artist to preserve the myth of his abandonment of naturalism.
While pondering this I found an obsessive Mondrian fetish site that has scans of all the flowers and all the late paintings grouped by color. Caution, this site is waa-a-ay pre-social media, with Comic Sans lettering and crisp HTML borders floating over a hideous textured yellow background.